Preheating Device

ABSTRACT

A preheating device intended for use in aluminothermic welding operations consists of a housing ( 12 ), which receives a nozzle ( 8 ) and is provided with a liquid gas feed ( 9 ), and a vaporizer ( 10 ), which is arranged downstream of the nozzle in the direction of flow, wherein the housing ( 12 ) has on its end facing a casting mould a combustion space, which ends in an outflow opening ( 11 ) for combustion gases and receives the nozzle, and a portion ( 22 ), which encloses the outflow opening ( 11 ) and can be inserted into an opening formed in the upper side of the casting mould, and wherein the vaporizer ( 10 ) is located between the outflow opening ( 11 ) and the nozzle ( 8 ), thereby being in heat exchange with the combustion gases.

The invention relates to a preheating device according to the preamble of claim 1.

When aluminothermic welding is carried out, it is usually necessary to preheat the rail ends, the enclosing halves of the casting mold that is used for welding, and the materials used for sealing, such as sealing paste or molding sand, before the molten steel is poured in, order to remove moisture and ensure that the rail ends are welded securely. For preheating, it is generally known to use the hot exhaust gases from burners in which a gaseous or liquid fuel is reacted with air or oxygen. Oxyfuel gas torches are regularly used for aluminothermic welding, and are operated with a gaseous fuel, such as a propane-butane mixture or pure oxygen and acetylene. Alternatively, burners are also known that are fuelled with gasoline and compressed air.

The disadvantage of preheating with gaseous fuels in this manner is the need to carry heavy, expensive gas cylinders which have to be equipped with a sophisticated pressure control. When torches fuelled with gasoline and compressed air are used, it is also necessary to carry a heavy, expensive compressed air unit, which furthermore requires an external power supply.

A preheating device intended for use in aluminothermic welding of two rail ends that can be placed on a casting mold enclosing the rail ends and is operable with liquid gas is known from WO 00/76713 A1. It consists of a frame that holds the gas cartridge and includes a burner, the outlet opening of which is located above an inlet opening of the casting mold, which consists of two mold halves. A copper vaporizer consisting of a vaporizer block with a solid body through which a line section passes and a spiral vaporizer section downstream therefrom in the direction of the gas cartridge is located between the gas cartridge and the burner. The efficiency of these burners relies to a large extent on ensuring that the liquid gas used enters the burner in a fully vaporized state. If the gas is incompletely vaporized or if liquid gas is discharged from the nozzle, not only is the heat output generated by the burner impaired, but this condition might also represent a safety risk for the environment.

Since aluminothermic welding is often carried out on the laid track, the effect of ambient temperature on the vaporizing process is unavoidable, thus leading to inadequate vaporization at lower temperatures. The use of such a preheating device for work on the laid track might thus be subject to weather-related restrictions.

When preheating the casting mold, the preheating device is operated in such manner that the hot combustion gases flow into the casting mold from the top, pass through the mold and finally exit through lateral channels. In this arrangement, a risk exists that upon exiting the mold said combustion gases may subsequently rise and mix with the air that intended for use in the combustion process of the burner, thereby reducing the heat output generated by the burner.

Document DE 40 21 819 A1 discloses a burner unit that is operable with liquid gas, equipped with a gas cartridge and intended particularly for brazing, and which consists of a pressure booster connected to a gas supply line and represented by a check valve, a vaporizer device with a brass body through which lines pass and which is connected to the booster, and a tubular combustion chamber that is designed for mixing with ambient air and encircles the outside of the vaporizer device. The objective of this device is particularly to achieve complete vaporization of the liquid gas by transferring the heat generated in the combustion chamber by the combustion process to the brass body via the metal jacket that surrounds the combustion chamber. It is intended for the burner output to be further supported by the fact that the gas enters the vaporizer device at a pressure that is determined by the characteristics of the check valve.

It is true that the pressure booster allows this known burner unit to be used in any position, but since the combustion chamber is equipped with lateral openings to enable combustion air to enter, when it is used vertically for aluminothermic welding it is impossible to reliably prevent the combustion gases that have flowed through the casting mold from being aspirated and reducing the heat output of the burner.

Against this background, it is the object of the invention to design a compact, powerful preheating device that is operable with gas, particularly liquid gas, requires no external power supply, is unaffected by weather conditions and is usable without having to be accompanied by complicated, expensive, heavy ancillary equipment. Said object is solved for such a preheating device by the features described in the characterizing part of claim 1.

Accordingly, the preheating device comprises a combustion chamber arranged immediately upstream of an outflow opening for the combustion gases, the vaporizer being located in this chamber and is thus in heat exchange with the combustion gases. In this way, the vaporizer, which is disposed between the nozzle and the outflow opening, is heated effectively so that vaporization of the liquefied gas can be achieved completely, reproducibly and regardless of weather conditions. The achievable heat output of the device is thus unaffected by an inconsistent degree of vaporization depending on the prevailing temperature conditions.

According to the features of claims 2 and 3, the housing has a portion on the underside thereof that encloses the outflow opening and is designed for insertion in the opening conformed in the facing upper side of the casting mold. The housing and therewith also the preheating device thus assume a defined operating position on the casting mold, which fixes the distance between the outflow opening and the upper sides of the rail ends to be welded. In this way it is ensured that identical preheating conditions are always provided during repeated use of the preheating device. Said section is preferably secured in the opening in form-locking manner, so that a reliable, stable operating position is established. However, other arrangements for securing the connection known to a person skilled in the art are also possible. In its simplest form, said opening may be the pouring inlet for the casting mold.

According to the features of claim 4, the housing of the device is provided with at least one laterally projecting pipe socket for bringing combustion air into the combustion chamber. The essential aspect of this feature is that combustion air which exists directly under ambient conditions is used, and is sucked in by the reduced pressure created by the combustion gases exiting through the outflow opening in the otherwise fully closed housing. Consequently, the device may be of relatively simple construction and it is also simple to operate, since in contrast to the prior art described in the introduction, it does not need to be supported with heavy, expensive ancillary apparatuses.

The features of claim 5 are directed to the further configuration of the housing, in this case the attachment point of the at least one pipe socket. Since this is arranged at a distance from the nozzle on the side thereof facing away from the outflow opening, the combustion chamber is characterized by uniform flow conditions that enable optimal mixing of combustion air and vaporized liquid gas.

According to the features of claim 6, the vaporizer is formed by a line arrangement that extends along the inner wall of the housing within the combustion chamber, and which is thus in surface contact with the combustion gases flowing through the core cross-section of the, for example, overall cylindrical housing for purposes of heat exchange.

According to the features of claim 7, the housing is constructed so that a liquid gas cartridge may be placed thereon, and a connection with the facing end of the liquid gas feed line is present here. Alternatively, however, a liquid gas line in general may also be connected at this point.

According to the features of claim 8, the lateral extension of the pipe socket intended for introducing combustion air is designed to ensure that effectively no combustion gases exiting laterally from a casting mold during a preheating process can be aspirated through the inflow opening thereof. This helps to support the maintenance of stable conditions in the combustion process and therewith a reproducible heat output.

The features of claim 9 are designed to achieve a possible increase in output of the burner by introducing extra combustion air in the housing by means of a fan. A battery-powered fan may be used for this purpose. This measure does increase the weight of the preheating device, but only slightly compared with a motorized compressor unit.

It may be seen that the preheating device according to the invention is a powerful apparatus that may be operated simply—that is to say it does not require cumbersome ancillary equipment—and independently of weather conditions, and is therefore particularly suitable for working on laid track.

In the following, the invention will be explained in greater detail with reference to the embodiment illustrated diagrammatically in the drawing. In the drawing:

FIG. 1 is a side view of the preheating device according to the invention mounted on a casting mold;

FIG. 2 is a side view of the preheating device in a plane I-II in FIG. 1.

Reference signs 1, 2 in FIG. 1 designate two rail ends to be welded together, the opposing frontal faces of which are separated by the welding gap and positioned inside a casting mold 3 that comprises to mold halves 4, 5 (FIG. 2). Casting mold 3 encloses a casting cavity in known manner, which casting cavity has a pouring opening and ventilation openings in upper side 6 thereof, which are in continuous communication with each other via the casting cavity. Reference sign 7 designates a preheating device according to the invention, comprising a nozzle 8, a liquid gas feed 9 and a vaporizer 10, wherein all said components are arranged in a generally cylindrical housing 12, the lower side of which forms an outflow opening 11.

Housing 12 forms a portion 22 in the area of outflow opening 11 in an opening formed in upper side 6 of casting mold 3 may be inserted and is secured in form-locking manner therein. This opening may be said pouring opening—but another opening is also conceivable. In this way, housing 12 is mounted securely, and a further advantage is obtained in that outflow opening 11 is positioned at a reproducible distance above the rail surface, thus assuring correspondingly reproducible preheating conditions.

Housing 12 and liquid gas feed 9 may be connected to one another in known manner via a liquid gas cartridge, not shown in the drawing.

Reference signs 13, 14 designate two pipe sockets projecting radially from housing 12, the free ends of which form inflow openings for combustion air and which are in continuous communication with the interior of housing 12.

Discharge opening 15 of nozzle 8 is located inside housing 12 and at a distance before outflow opening 11, so that a combustion chamber is defined thereby and nozzle 8 is connected to vaporizer 10 that is formed by a pipe line routed spirally in the peripheral region along the inner side of housing 12 in such manner that the liquid gas routed through liquid gas feed 9 first enters vaporizer 10, which extends along the side size of nozzle 8 that faces outflow opening 11, and thus inside the combustion chamber, is vaporized thereby, and enters housing 12 in this state via discharge opening 15 of nozzle 8. In housing 12, said gas is mixed with the combustion air entering via pipe sockets 13, 14, which results in the formation of a combustible gas-vapor mixture, by which the heat is generated after the combustion process is started, and which also supports the vaporization of the liquid gas in vaporizer 10.

The outflow of combustion gases through outflow opening 12 creates reduced pressure conditions inside housing 12, which helps to encourage the aspiration of combustion air via pipe sockets 13, 14.

Apart from pipe sockets 13, 14 and outflow opening 11, housing 12 has a closed construction.

The combustion gases that are discharged via outflow opening 11 pass through the described opening in the casting mold and into the casting cavity thereof in the direction of arrow 16, thus in the form of a burner flame 17 that is directed vertically downwards. The combustion gases flow through the casting cavity, transferring heat to the walls thereof and evaporating any moisture present, and then exit through lateral ventilation openings, again rising substantially vertically in the direction of arrows 18, 19.

The length of pipe portions 13, 14, that extend radially relative to housing 12 is fixed on the base of the usual dimensions of casting mold 3, particularly the upper side ventilation openings thereof, in such manner that the inflow openings thereof lie outside a region in which combustion gases can still be sucked in. This means that the combustion air introduced into pipe portions 13, 14 in the direction of arrows 20 is suitable for creating ideal combustion conditions inside housing 12, so that an optimally combustible gas-vapor mixture is created with the liquid gas escaping from discharge opening 15 of nozzle 8 in vapor form. Burner flame 17 passes through the casting cavity in casting mold 3 from top to bottom, and then emerges from any of said ventilation openings in the upper side in the form of a flame 21.

Since vaporizer 10—seen in the direction of flow of the combustion gases—is connected immediately after the portion accommodating nozzle 8 inside housing 12, and thus inside said combustion chamber in which the combustion process is initiated, it is ensured that sufficient heat is provided for the operation of vaporizer 10, so that it is always possible for the liquid gas to be completely vaporized regardless of the prevailing weather.

To further improve the performance of the preheating device, additional combustion air may be introduced into housing 12 through at least one of the pipe sockets 13, 14 by means of a battery-powered fan.

LIST OF REFERENCE SIGNS

-   1. Rail end -   2. Rail end -   3. Casting mold -   4. Mold half -   5. Mold half -   6. Upper side -   7. Preheating device -   8. Nozzle -   9. Liquid gas feed -   10. Vaporizer -   11. Outflow opening -   12. Housing -   13. Pipe socket -   14. Pipe socket -   15. Discharge opening -   16. Arrow -   17. Burner flame -   18. Arrow -   19. Arrow -   20. Arrow -   21. Flame -   22. Portion 

1-9. (canceled)
 10. A preheating device for casting mold (3) for use in aluminothermic welding, comprising a housing (12) that receives a nozzle (8) and is provided with a liquid gas feed (9), and a vaporizer (10) that is arranged upstream of the nozzle (8) in the direction of flow of the liquid gas, characterized in that the housing (12) has a combustion space which ends in an outflow opening (11) for combustion gases and accommodates the nozzle (8) at the farthest end thereof in the direction of flow, that the vaporizer (10) is located between the outflow opening (11) and the nozzle (8), thereby being in heat exchange with the combustion gases, that the housing (12) is furnished with at least one laterally projecting pipe socket serving (13, 14) to introduce combustion air under ambient conditions, and which protrudes laterally from the housing (12) in such manner that at least no substantial aspiration of combustion gases rising out of the casting mold (3) takes place.
 11. The preheating device according to claim 10, characterized in that the pipe socket (13, 14) is attached at such a point of the housing (12) that is located on the side of the housing (12) facing away from a discharge opening (15) of nozzle (8).
 12. The preheating device according to claim 10, characterized in that the vaporizer (10) is represented by a line that runs along the inside of the housing (12) and is in surface contact with the combustion gases for heat exchange.
 13. The preheating device according to claim 10, characterized in that the housing (12) is designed so that a gas cartridge can be mounted thereon, and can be connected to the liquid gas feed (9).
 14. The preheating device according to claim 10, characterized in that at least one of the pipe sockets (13, 14) is operatively connected to a fan that is designed for the purpose of introducing additional combustion air into the housing (12).
 15. The preheating device according to claim 11, characterized in that the vaporizer (10) is represented by a line that runs along the inside of the housing (12) and is in surface contact with the combustion gases for heat exchange.
 16. The preheating device according to claim 11, characterized in that the housing (12) is designed so that a gas cartridge can be mounted thereon, and can be connected to the liquid gas feed (9).
 17. The preheating device according to claim 12, characterized in that the housing (12) is designed so that a gas cartridge can be mounted thereon, and can be connected to the liquid gas feed (9).
 18. The preheating device according to claim 11, characterized in that at least one of the pipe sockets (13, 14) is operatively connected to a fan that is designed for the purpose of introducing additional combustion air into the housing (12).
 19. The preheating device according to claim 12, characterized in that at least one of the pipe sockets (13, 14) is operatively connected to a fan that is designed for the purpose of introducing additional combustion air into the housing (12).
 20. The preheating device according to claim 13, characterized in that at least one of the pipe sockets (13, 14) is operatively connected to a fan that is designed for the purpose of introducing additional combustion air into the housing (12). 